Preparation of azo compounds



2,711,405 a I PREPARATION on zo c moms Arthur William Anderson, Verona, N. J.,jassign ojr to E. I. du Pont de Nemours & Company, Wilmington, Del.,acorporationf Delaware i No Drawing. Application April 5, 1949,

Serial No. 85,720 I i 12 Claims. (Cl. 2 0-192 This invention relates to the preparation of azo compounds 'and, more particularly, to the preparation of azo compounds useful as polymerization catalysts, I i

In the preparation of a great number ofa' zo com pounds particularly the type of azo compounds useful as polymerization catalystsdisclosed in Hunt U. S. Patent 2,471,959 patented May 31, 1949, hydrazine and deriv atives thereof have been used as raw materials. Since hydrazine is a relatively expensive raw material, use of this compound or derivatives thereof in the preparaa, "This example illustratesl theifpreparation 0f" alpha, I

tion of various azo compounds contributes substantially to the cost of the final product. The preparation of various azo compounds 'using hydrazine orderivatives thereof as a 'raw material is described in Thiele and Heuser, Ann. 290, l-43 (1896); Hartmann, Rec. trav. 1

chim. 46, 150453 (1927); Chem. Weekblad, vol. 2'3, pages 77-78, January '1926; and Dox, J. Am. Chem. Soc. 47, 1471-1477, 1925.

An object of the present invention is to provide a new and improved process for the preparation of azo compounds wherein theazo, N=N--, group is bonded from both of the nitrogens to difierent'tertiarycarf bon atoms. A further object is to provide a new and improved process for the preparation of azo compounds.

useful as polymerization catalysts. A still further object is to provide a low cost processfor producingazo compounds by using starting compounds other than hydrazine or derivatives thereof.' Further objects will be apparent from the description of the invention given hereinafter.

W Ttill'e'd under reduced 'pressureJ The fraction boiling "between 50 and 60 C. at ISL-l9imillimetersl-pressure was;

alpha-aminoisobutyronitrilex-which amounted "to70 of the t heor etiQal yield. v i i In a preferred formthe' alpha-amino' compound used is one having the general 'f i I l l R gi /A I no i 'wherein'A represents a radicalfrom the group consisting: of .CN, -COO M, and COOR, Rybeing an alkyl radi v cal having 1 to 6 carbon atoms, inclusive, and M an alkali";v metal, and R and R are hydrocarbon radicalsgpreferalily 7 containing from ,1 to '6 carbon atoms, inclusive'jlAlso, it is preferred to carryv out-the-reaction at a temperature be tween +20 Cland 10.C. and, even'more specifically,

between 77100 C. and-+53. C., and to use sodium hypo? chlorite;

A I The following enample in which allpartsgbyhweight' i unless otherwisespecified, illustrates-a specific embodiment 1 J of the present invention, 7

Example -11 alpha-azodiisobutyronitrile from xalpha-aminoisobutyronitrile,"

inJacohsom'J. A. c. $.68, 262 8 (1946 1 One'molel(85 grams) of acetone cyanhydrinand two. moles of ammonia were mixed in a steel reactionvessel and wereshaken.together-for four hours... .Thereaction iesselfwasplac ed in an ice bath toconduct theexothermic I heat from the reaction. At the end of fourihour s excess ammonia was bled 101T ,and' the remainingliquid ;was dis Three-tenths at a moie 12 grams) of sbdiiidhydr'diide dissolved inf'6i). cc," of water. were poured into an Erlena meye'r flask. Chlorine was passed-in atarteniperature-ofj j about 0 C.1iutil;ab out-0. 13 rnole (8.8 grams) had been 1 absorbed. Eight and]; four-tenths grams; of the alpha- The above objects are' accomplished according to the pound having the general formula R4 NHz wherein A is a radical from the group consisting of present invention by dissolving an alpha-amino com? CN, COOM, and COOR, R being an alkyl' radical and M an alkali metal or alkaline earth metal, and- R and 'R" are radicals from the group consisting of aminoisobutyronitrile, was rapidly Zadded to the hypo chlor-ite solution thus formed which also contained 125 grants ofcrushedice. The mixture lwhich was maintained at a" temperature of'ahout 8.. C. wasagita'ted for about :I8 10' m'inutesl The reaction resulted in the formation of. ai finely diyided, whitefcrystallirie' precipitate; which hydrocarbon and alkoxy hydrocarbon, radicals, in an aqueous solution of a compound from the group consisting of the alkali metal and alkaline earth metal hypo halites, at a temperature below 10 C. and separating the reaction product formed from the solution.

case R and R", in a sense, represent only a single cyclic radical joined through two separate, discrete carbon atoms in the cyclic radical to the carbon atom which .The radicals R and R" may be two separate'radicals or they may be combined to form a cyclic radical in which was [immediately removedfby {,filtrationi thoroughly fwashe'diwith distilled water, air driedfand' vacuum jdried. j" The yieldf offalp ha; alpha azodiisobutyronitrile weighed 3 I .L 6.81 grams: whichis 85%;of the theoretical yield. The -'product melted at 1105-101" 0. 2 1 1 r V The above reactions'takel-place accordingato the fol lowing'equations: r L.

is joined to the NH2 group. Hence, in'the" above gene'ral V formula R and R" include both separate radicals and, combined, a single cyclic radical. Morespecifically, where R and R" are combined in a cyclic radical, the alpha amino compounds of the general formula CHE-.114 NHz are preferred.

in 'Jacobson, L'ALQ S. 68, 2628 (1946), for example, alpha amino -,alpha,-methyl=- gamma m'ethylvaleroni j It:will understood that theabove exampleis-merely; illustrative and-the'invention broadly comprises dissolving;

an-alpha-aminocompound fofathe type-disclosed in an aqueous solution of an. alkali metal or alkaline earth' 7 metal hypohalite ata temperaturebelow 10; C."and sepi arati ng theazo compound formed,,-from -.the solution. Qther alpha-amino compounds of the type disclosed. may be prepared'by adaptation'softhe method described V 2,711,405 a paten d: Jam; .2'1,;-1g55 The alpha-aminoisobutyronitrile was prepared inthefol a lowing manner according to the general method described I trile; alpha-aminomethylisobutyrate; alpha-aminocyclohexanecarbonitrile; alpha amino alpha methyl gamma-methyl gamma methoxyval ronitrile; and alphaaminoalpha-phenylpropionitrile, which alpha amino compounds may then, in accordance with the present invention, be dissolved in sodium hypohalite and the reaction carried out under conditions analogous to those in Example I to obtain alpha,alpha-azobis (alpl'iagarrimadimethylvaleronitrile); dimethyl alpha,alpha-azodiisobutyrate; 1,1 azodicyclohexane-carbonitrile; alpha,- alpha'-azobis (alpha,gamma-dimethyl-garnma-meth valeronitrile); and alpha,alpha-azobis (alpha-phenylpropionitrile) respectively.

Proportions of the reactants are not critical although, in general, approximately stoichiometric proportions will be used as a matter of efiiciency and economy. It has been found that a slight excess of the alkali metal or alkaline earth metal hydroxide over that required to react with the halogen used is of some advantage since the presence of excessive or free halogen tends to have a somewhat deleterious effect on the reaction. Also, an excess of the alkali metal or alkaline earth metal hypohalite over that required to react with the alpha-amino compound, is slightly preferred. Any type of reaction vessel may be used although it should be equipped with means for agitating the contents. A high speed rotary type of mixer is preferred.

The reaction is best carried out in the absence of contaminating elements such a various heavy metals, especially iron and copper, which tend to decompose the hypohalite solution. in the preparation of relatively low melting azo compounds, the reaction product will be in the form of an oily liquid rather than as a crystalline precipitate, so that it is necessary to isolate the azo compound by crystallization from a solvent solution. Where the azo compound is formed as a crystalline precipitate, it may readily be removed from the solution by filtering.

A condition of this invention is that the alpha-amino compound be dissolved in the hypohalite solution at a temperature below C. At temperatures appreciably above 10 C., there may be some reaction and some azo compound formed but the reaction gives poor yields and it is not practical to operate above 10 C. There is no limit to the lower temperature except the mechanical one of avoiding trouble through freezing. It is hard to conceive conditions warranting going below 4 C. and, practically, 2(l C., is about the lower limit. It is preferred to carry out the reaction at a temperature between 10 C. and +5" C. The expedient of intro ducing crushed ice into the hypohalite solution to form an ice-hypohalite slurry is a convenient method of maintaining a desirable temperature. However, the reaction vessel may be surrounded externally by a low temperature medium.

Any alkali metal or alkaline earth metal hypohalite may be used in carrying out the present invention although the hypochlorites, being most economical and highly active in this reaction, are preferred. The hypobromites and hypoiodites are less preferred but operable. The metal salt of the hypochlorite may be any of those shown in the examples, i. e., sodium, potassium and calcium, or other such metals as lithium, strontium, or barium but sodium hypochlorite, the most economical hypohalite, is the preferred one as the reaction proceeds very rapidly when using it.

The alpha-amino compounds having the general formula It A R NH? wherein A represents a radical from the group consisting of -CN, -COOM, and COOR, R being an alkyl radical and M an alkali metal or an alkaline earth metal, and R and R" are radicals from the group consisting of hydrocarbon radicals, including aliphatic, alicyclic, and aromatic hydrocarbon radicals, and alkoxy hydrocarbon radicals, may be prepared by adaptations of the methods described in the following references: Dubsky and Wensink, Ber. 49, 1134 (1916); Bucherer and Steiner, l. Prakt. Chem. 140, 308 (1934); and Jacobson, J. A. C. S. 67, 1996 (1945); as well as the above-mentioned Jacobson, J. A. C. S. 68, 2628 (1946).

The azo compounds prepared in accordance with the method of the present invention are those wherein the azo, -N=N, group is bonded from both of the nitrogens to diiferent tertiary carbon atoms from the group consisting of aliphatic and cycloaliphatic carbon atoms, both of said different carbon atoms being tertiary and one of the carbon atoms bonded to each of said tertiary carbon atoms ha ing its remaining valences satisfied only by elements of the class consisting of oxygen and nitrogen. Among these azo compounds in addition to those already mentioned are alpha,alpha'-azobis (alpha-methylbutyronitrile); alpha,alpha'-azobis (alpha-ethylbutyro- .itrile); alpha,alpha-azobis (alpha-cyclopropyl-propionitrile); alpha,alpha-azobis (alpha-cyclohexyl-propionitrile); alpha,alpl1a'-azobis (alpha-cycloheptylpropionitriie; alpha,alpha-azobis (alpha-isopropyl-beta-methylbutyronitrile); alpha,alpha-azobis (alpha,gamma-dimethylcapronitrile) alpha,alpha'-azobis (alphwmbutylcapronitrile); alpha,alpha'-azobis (alpha-isobutyl-gamrna' methylvaleronitrile) l, l '-azodicycloheptanecarbonitrile, and the corresponding esters of the above in which the nitrile groups are replaced by ester groups, e. g., dimethyl, diethyl and dihexyl alpha,alpha-azodiisobutyrate, and the corresponding compounds in which the nitrile group is replaced by COOM, M being an alkali metal or;

alkaline earth metal.

The concentration of the aqueous hypohalite solution is not critical although the use of a concentrated solution is more convenient and economical to handle. That is, the reaction can be carried out using dilute solutions but the greater volume of liquids necessarily involves larger equipment and general inconvenience. There should be sutlicient liquid. present to facilitate removal of the reaction product but such quantity of liquid is inherently present in any aqueous solution of these hypohalites.

The formation of the herein considered azo compounds depends on the alpha-amino compound dissolving in the aqueous hypohalite solution. Most of the alpha-amino compounds coming within the scope of this invention will immediately dissolve in the hypohalite solution. However, some alpha-amino compounds are only sparingly soluble in the hypohalite solution; this involves no practical difficulty in carrying out the process as the alphaamino compound will progressively dissolve in the hypohalite solution as the azo compound is formed and precipitated. it will merely require a longer period to dissolve all the alpha-amino compound if it is of limited solubility in the hypohalite solution.

The outstanding advantage of the present invention is that it provides such a simple and economical process of preparing these azo compounds as compared to the prior art process of preparing these azo compounds from hydra- Not only are the alpha-amino compounds a relazines. tively cheap raw material compared to the hydrazines but the yields obtained are very high and the procedural steps are readily carried out.

As many apparently widely different embodiments'of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. Process of preparing azo compounds wherein the azo, -N=N, group is bonded from both the nitrogens to different tertiary C atoms each of which has bonded thereto one cyano, CN, group, which processcomprises dissolving an alpha-amino compound having the general formula R \NH2 wherein R and R" are radicals from the group consisting of hydrocarbon and alkoxy hydrocarbon radicals, in an aqueous solution of a compound from the group consisting of the alkali metal and alkaline earth metal hypohalites, at a temperature below +10 C. and separating the reaction product formed from said solution.

2. Process as set forthin claim 1 whereinR and R" are hydrocarbon radicals.

3. Process as set forth in claim 1 wherein R is an'alkyl radical containing from 1 to 6 carbon. atoms, inclusive, and R and R". are hydrocarbon radicals l to 6 carbon atoms, inclusive. l

4. Process as set forth in claim 1 wherein said alphaamino compound is alpha-aminoisobutyronitrile.v

5. Process as set forth in claim- 1 wherein said alphaamino compound is dissolved in an aqueous solution of an alkali metal hypochlorite.

6. Process as set forth in claim 1 wherein said alphaamino compound is dissolved in an aqueous solution of an alkali metal hypochlorit'e at a temperature between -20 C. and +10 C.

7. Process as set forth in claim 6 wherein perature is between 10 Ciand +5 C.

8. Process of. preparing alpha,alpha'-azodiisobutyronitrile which comprises dissolving 'alpha,aminoisobutyronitrile in an aqueous solution of an alkali metal jhypochlocontaining from.

. rite at a temperature between 20 C. and-HO C. and

separating the crystalline precipitate formed from said temperature between 1.02 C. to |'5 C- separating said temthe crystalline precipitate formedfro'm;saidsolution.

10.: Process of preparing alpha,alpha-azodiisobutyt0ni; trile" which comprises reactingl alpha-aminoisobutyroni? trile .inan aqueous solution'with sodium hypochlorite at a a a temperature of about 0 .C.

I 11-. Process of preparing alpha,alpha@azodiisobutyronhtrile whic'hcorr'rprises reacting alpha-aminoisobutyroni-f trile in anaqueous solution with a hypochlqr'ite selected from the groupconsisting'of alkali metalfand alkaline I earth metal hypochlorites at a temper'atureofabout 0 C...

12. Process of preparing alpha,alpha aaodiisobutyroni trile which comprises reacting 'al pha amirioisobutyronfl- I trile inan'aqueous solution withfa,hypochloritefselected fr orn the groupjconsistingtof alkali m'etaI and alkaline earth .metal hypochlorites "at ;a. temperature' 1be'tween" Lieben 'et s13 Chemical :Abstracts, v. 27;. 133; page -42s9.=- 

1. PROCESS OF PREPARING AZO COMPOUNDS WHEREIN THE AZO, -N=N-, GROUP IS BONDED FROM BOTH THE NITROGENS TO DIFFERENT TERTIARY C ATOMS EACH OF WHICH HAS BONDED THERETO ONE CYANO, -CN, GROUP, WHICH PROCESS COMPRISES DISSOLVING AN ALPHA-AMINO COMPOUND HAVING THE GENERAL FORMULA 